rnapshot is an excellent backup application and has been around for a long time and is extremely stable. This article discusses doing backups to an external USB drive that is formatted for the "ext3" filesystem type. It depends on the attributes that are unique to Linux/Unix (i.e. ext3, ext4) filesystems only. If backups to CIFS (Samba a.k.a. smb, fat, fat32, vfat, ntfs) filesystems are required a different backup application '''must''' be used (i.e. rdiff-backup).